Micromachined devices (also called micromechanical devices or microelectro-mechanical devices) are small (micron scale) machines that are constructed using semiconductor processing techniques. Micromachines include a variety of devices, such as fluid control devices (e.g., valves and pumps), motors, and gear trains analogous to conventional macroscale machinery. As used herein, the term micromachine refers to any three-dimensional object that is at least partially constructed in reliance upon semiconductor processing techniques.
FIG. 1 illustrates a micromachined valve 20 constructed in accordance with the prior art. The valve 20 includes three major components: a heat insulating substrate 22, a deformable membrane 24, and a fluid routing substrate 26. The heat insulating substrate 22 may be formed of Pyrex, while the deformable membrane may be formed of silicon. A working fluid 28 is positioned in a void formed between the heat insulating substrate 22 and the deformable membrane 24. A thin-film heater 30 is formed on the heat insulating substrate 22. More particularly, as shown in FIG. 1, the thin-film heater 30 is attached to an interior surface of the valve 20. An electrical contact 32 and an electrical feedthrough 34 are used to supply current to the thin-film heater 30. Although not shown for the purpose of simplicity, at least one additional contact and electrical feedthrough are also used. FIG. 1 also shows a seal cap 36 which may be used to deliver the working fluid 28 into the valve 20.
The deformable membrane 24 is positioned on a pedestal 38 and carries a valve seat 40. The valve seat 40 rests over a valve opening 42. Thus, the apparatus of FIG. 1 represents a normally closed valve. That is, the valve of FIG. 1 is closed when no power is applied to it.
FIG. 2 illustrates the valve of FIG. 1 in an open state after power is applied to it. When current is applied across the thin-film resistor 30, the working fluid 28 is heated and subsequently expands, thereby deforming the deformable membrane 24. As a result, fluid can pass through the valve opening 42, as shown with arrow 44.
Those skilled in the art will recognize a number of shortcomings associated with the apparatus of FIGS. 1 and 2. First, the prior art device is relatively slow because it is relatively time-consuming to heat the working fluid 28 with the thin-film heater 30. In addition, the prior art device is relatively expensive to manufacture and test. A significant portion of this expense is associated with the thin-film heater 30. The thin-film heater 30 is inherently expensive to manufacture. Testing of the thin-film structure is difficult because of the position of the thin-film heater in the interior of the valve. Furthermore, it is relatively expensive to provide a thin-film heater with refined temperature and current control capabilities.
In view of the foregoing, it would be highly desirable to provide an improved micromachined fluid control device. Such a device should provide improved speed in controlling the temperature of the working fluid. In addition, such a device should be relatively inexpensive to manufacture and test.